WO2022210297A1

WO2022210297A1 - Magnetic marker detection method and system

Info

Publication number: WO2022210297A1
Application number: PCT/JP2022/014132
Authority: WO
Inventors: 道治山本; 知彦長尾; 均青山
Original assignee: 愛知製鋼株式会社
Priority date: 2021-04-01
Filing date: 2022-03-24
Publication date: 2022-10-06
Also published as: CN117083214A; EP4318436A1; JP2022158105A; KR20230165268A

Abstract

Provided is a marker detection system (1) that enables a vehicle (5) comprising a magnetic sensor to detect a magnetic marker (10) disposed on a road surface (100S) which forms the surface of a travel road (100). The magnetic sensor is capable of measuring, for each of the following axes, the size of a magnetic component acting along a vertical-direction axis and a traveling-direction axis. A detection unit (12) specifies, on the basis of changes which are in the traveling direction of the vehicle (5) and which are in a magnetic measurement value along one of the axes, a candidate section in which the magnetic marker (10) is likely to be present, and determines whether the magnetic marker (10) has been detected according to a degree of synchronization of a first signal, which represents a change in the candidate section of the magnetic measurement value for one axis, and a second signal, which represents a change in the candidate section of the magnetic measurement value for the other axis.

Description

Magnetic marker detection method and system

The present invention relates to a method and system for detecting magnetic markers arranged on the track of a vehicle.

Conventionally, there has been known a magnetic marker detection system for vehicles that uses magnetic markers arranged on roads for vehicle control (see Patent Document 1, for example). Using such a magnetic marker detection system, for example, if the magnetic markers placed along the lane can be detected by the vehicle's magnetic sensor, etc., various types of driving assistance such as automatic steering control, lane departure warning, and autonomous driving can be realized. can.

Japanese Patent Application Laid-Open No. 2005-202478

However, the above conventional magnetic marker detection system has the following problems. That is, there is a problem that the reliability of detection of the magnetic marker may be impaired due to various disturbance magnetism acting on the magnetic sensor or the like. For example, vehicles running side by side or vehicles passing each other can also be sources of disturbance magnetism.

The present invention has been made in view of the conventional problems described above, and aims to provide a magnetic marker detection method and system with high detection certainty.

One aspect of the present invention is a method for detecting magnetic markers disposed on a road surface forming a surface of a track while a vehicle equipped with a magnetic sensor is moving on the track, comprising:
The magnetic sensor is capable of measuring magnitudes of magnetic components acting along a plurality of axes including at least two axes for each of the plurality of axes,
A candidate section, which is a temporal or spatial section to which the magnetic marker is likely to belong, based on a change in the traveling direction of the vehicle in the magnitude of the magnetic component along at least one of the plurality of axes. a first process of identifying
A first signal representing a change in the candidate interval of the magnitude of the magnetic component acting along one of the two axes and the candidate interval of the magnitude of the magnetic component acting along the other axis. and a second process of determining whether or not the magnetic marker is detected in the candidate section according to the degree of synchronization.

One aspect of the present invention is a system for a vehicle equipped with a magnetic sensor to detect a magnetic marker disposed on a road surface forming the surface of a road,
The magnetic sensor is capable of measuring magnitudes of magnetic components acting along a plurality of axes including at least two axes for each of the plurality of axes,
A candidate section, which is a temporal or spatial section to which the magnetic marker is likely to belong, based on a change in the traveling direction of the vehicle in the magnitude of the magnetic component along at least one of the plurality of axes. a first circuit that identifies
A first signal representing a change in the candidate interval of the magnitude of the magnetic component acting along one of the two axes and the candidate interval of the magnitude of the magnetic component acting along the other axis. and a second circuit for determining whether or not the magnetic marker is detected in the candidate section according to the degree of synchronization.

The present invention is premised on a vehicle equipped with a magnetic sensor capable of measuring the magnitude of magnetic components acting along a plurality of axes, including at least two axes, for each axis. The present invention provides a combination of a first process or circuit for identifying a candidate section to which a magnetic marker is likely to belong, and a second process or circuit for determining whether or not the magnetic marker has been detected in the candidate section. It has one of the technical features.

A first process or circuit identifies the candidate section based on a change in the traveling direction of the magnitude of the magnetic component along at least one of the plurality of axes. A second process or circuit generates a first signal representing a change in the candidate interval in the magnitude of a magnetic component acting along one of the two axes and a magnetic field acting along the other axis. It is determined whether or not the magnetic marker has been detected according to the degree of synchronization between the second signal representing the change in the magnitude of the component in the candidate interval.

In the present invention, first, candidate sections to which magnetic markers are likely to belong are identified. Then, it is determined whether or not the magnetic marker has been detected for each candidate segment to which the magnetic marker is likely to belong, using the degree of synchronization between the first signal and the second signal. According to the present invention, by providing the two steps of specifying the candidate section and determining whether or not the magnetic marker is detected in the candidate section, the detection of the magnetic marker can be reliably performed. It is possible to improve the quality.

FIG. 4 is a front view showing how the vehicle detects magnetic markers in the first embodiment; FIG. 2 is a top view showing a vehicle traveling in a lane on which magnetic markers are arranged according to the first embodiment; 1 is a configuration diagram of a marker detection system in Example 1. FIG. 4 is a flowchart showing the flow of marker detection processing in the first embodiment; FIG. FIG. 4 is an explanatory diagram showing a change in the traveling direction of a magnetic measurement value (Gv) in the vertical direction in Example 1; FIG. 4 is an explanatory diagram showing a change in the traveling direction of the magnetic measurement value (Gt) in the traveling direction in Example 1; FIG. 4 is an explanatory diagram of candidate sections in the first embodiment; FIG. 4 is an explanatory diagram showing a change in the traveling direction of the time difference value of Gv in Example 1; FIG. 4 is an explanatory diagram showing a change curve (distribution curve) of Gv in the vehicle width direction in the first embodiment; FIG. 4 is an explanatory diagram showing a change curve (distribution curve) in the vehicle width direction of the magnetic gradient in the vehicle width direction in the first embodiment; FIG. 5 is an explanatory diagram showing a change in the travel direction of the magnetic measurement value (Gh) in the vehicle width direction in the first embodiment;

Embodiments of the present invention will be specifically described using the following examples.
(Example 1)
This example relates to a detection method and system 1 for detecting a magnetic marker 10 laid on a road. This content will be described with reference to FIGS. 1 to 11. FIG.

This example is an example in which a marker detection system (an example of a system) 1 for detecting magnetic markers 10 is applied to a driving support system 5S that enables lane keeping driving. The driving support system 5S includes a vehicle ECU 50 that controls a steering actuator (not shown) for steering wheels, a throttle actuator for adjusting engine output, and the like. The vehicle ECU 50, for example, controls the vehicle 5 so that the amount of lateral deviation with respect to the magnetic marker 10 approaches zero, thereby achieving lane keeping running.

The marker detection system 1 is configured by combining a sensor unit 11 including a magnetic sensor Cn (n is an integer from 1 to 15) and a detection unit 12 that executes marker detection processing for detecting the magnetic marker 10. there is Hereinafter, after the magnetic marker 10 is outlined, the sensor unit 11 and the detection unit 12 that constitute the magnetic marker detection system 1 will be described.

The magnetic markers 10 are road markers that are arranged, for example, every 2 m along the center of the lane 100 that forms the course of the vehicle 5 . This magnetic marker 10 has a columnar shape with a diameter of 20 mm and a height of 28 mm, and can be accommodated in a hole provided in the road surface 100S. The magnetic marker 10 is a ferrite plastic magnet, which is a permanent magnet in which magnetic particles of iron oxide, which is a magnetic material, are dispersed in a polymer material, which is a base material. For example, a resin mold layer may be provided on all or part of the surface of the magnetic marker 10, which is the ferrite plastic magnet itself.

The maximum energy product (BHmax) of the ferrite plastic magnet forming the magnetic marker 10 is 6.4 kJ/cubic meter. The magnetic flux density of the end surface of the magnetic marker 10 is 45 mT (millitesla). Here, various types of vehicles such as passenger cars and trucks are conceivable as vehicles using magnetic markers. The mounting height of the magnetic sensor depends on the ground clearance for each vehicle type, and is generally assumed to be in the range of 100 to 250 mm. The magnetic marker 10 can apply magnetism with a magnetic flux density of 8 μT (8×10 −6 T) to a position with a height of 250 mm, which is the upper limit of the range assumed for the mounting height of the magnetic sensor Cn.

Next, the sensor unit 11 and detection unit 12 that make up the marker detection system 1 will be described.

The sensor unit 11 is a bar-shaped unit in which 15 magnetic sensors C1 to C15 are arranged in a straight line, as shown in FIGS. The intervals between the fifteen magnetic sensors C1 to C15 are equal intervals of 10 cm. The sensor unit 1 is attached, for example, inside a front bumper of the vehicle 5 with its longitudinal direction extending along the vehicle width direction. In the case of the vehicle 5 of this example, the mounting height of the sensor unit 11 with respect to the road surface 100S is 200 mm. The sensor unit 11 includes a combination of 15 magnetic sensors Cn and a signal processing circuit 110 containing a CPU (not shown) and the like (FIG. 3).

The magnetic sensor Cn is a sensor that detects magnetism using the well-known MI effect (Magneto Impedance Effect), in which the impedance of a magnetosensitive material such as an amorphous wire changes sensitively according to an external magnetic field. The magnetic sensor Cn detects a magnetic component acting along a magnetosensitive body such as an amorphous wire, and outputs a sensor signal representing the magnitude of the magnetic component (magnetism measurement value).

The magnetic sensor Cn is a highly sensitive sensor with a magnetic flux density measurement range of ±0.6 millitesla and a magnetic flux resolution of 0.02 microtesla within the measurement range. As described above, the magnetic marker 10 can apply magnetism with a magnetic flux density of 8 μT (8×10 −6 T) or more in the range of 100 to 250 mm assumed as the mounting height of the magnetic sensor Cn. A magnetic marker 10 that exerts magnetism with a magnetic flux density of 8 μT or more can be reliably detected using a magnetic sensor Cn with a magnetic flux resolution of 0.02 μT.

It should be noted that the magnetic sensor Cn of this example has a pair of magnetosensitive bodies that are perpendicular to each other so as to detect magnetic components acting in directions of two axes that are perpendicular to each other. Each magnetic sensor Cn is incorporated in the sensor unit 11 so that the directions of the pair of magnetosensitive bodies are the same. The sensor unit 11 detects a magnetic component acting along an axis in the direction of travel (one axis) and a magnetic component acting along an axis in the vertical direction (the other axis, an axis perpendicular to the direction of travel). Each magnetic sensor Cn is attached to the vehicle 5 so that it can be detected.

The signal processing circuit 110 (FIG. 3) is a circuit that performs signal processing such as noise removal and amplification on the sensor signal of each magnetic sensor Cn. The signal processing circuit 110 takes in the sensor signal of each magnetic sensor Cn every time the vehicle 5 travels a predetermined amount (for example, 5 cm), generates a corresponding magnetic measurement value, and inputs it to the detection unit 12 . As described above, the signal processing circuit 110 outputs the magnetic measurement value (Gv) representing the magnitude of the magnetic component acting along the vertical axis and the magnitude of the magnetic component acting along the traveling direction axis. A magnetic measurement (Gt), which represents In the following description, it is appropriately described as a magnetic measurement value of the magnetic sensor.

The detection unit 12 is a circuit that controls the sensor unit 11 and executes marker detection processing, which is arithmetic processing for detecting the magnetic marker 10 . The detection unit 12 has a circuit board on which a CPU (central processing unit) that executes various calculations, memory elements such as ROM (read only memory) and RAM (random access memory), and the like are mounted.

A work area for storing time-series magnetic measurement values of each magnetic sensor Cn is formed in the storage area of the RAM. The detection unit 12 uses this work area to store time-series magnetic measurement values over a past predetermined distance (for example, 10 m) corresponding to the movement history of the vehicle 5 .

A signal line of a vehicle speed sensor provided in the vehicle 5 is connected to the detection unit 12 . A vehicle speed sensor is a sensor that outputs a pulse signal each time a wheel rotates by a predetermined amount. The predetermined amount includes, for example, predetermined angles such as 1 degree, 10 degrees, and 30 degrees, and predetermined distances such as 1 cm, 5 cm, and 10 cm. The detection unit 12 of this example controls the sensor unit 11 so as to output magnetic measurement values (Gv, Gt) each time the vehicle 5 travels 5 cm.

The detection unit 12 reads the magnetic measurement values (Gt, Gv) from each magnetic sensor Cn stored in the work area of the RAM, and executes marker detection processing and the like. The result of the marker detection processing by the detection unit 12 includes the fact that the magnetic marker 10 has been detected and the amount of lateral deviation with respect to the detected magnetic marker 10 . The detection unit 12 executes a marker detection process every time the vehicle 5 advances (every time it moves) by 5 cm, and inputs the detection result of the marker detection process to the vehicle ECU 50 . As described above, the detection result by the detection unit 12 is used for various controls on the vehicle 5 side, such as automatic steering control for lane keeping, lane departure warning, and automatic driving. In this example, the marker detection process is executed once each time the vehicle 5 moves 5 cm, but the marker detection process may be repeatedly executed at a frequency of 3 kHz, for example.

The detection unit 12 has functions as the following circuits (means).
(a) First circuit: A candidate section to which the magnetic marker 10 is likely to belong is identified based on the change in the direction of travel of the vehicle 5 in the magnetic measurement value (Gt) in the direction of travel (first processing). The candidate section may be a temporal section sandwiched between two time points, or a spatial section between two points.
(b) Second circuit: Determines whether or not the magnetic marker 10 is detected in the candidate section (second processing). The second circuit provides a first signal representing a change in the vertical magnetic measurement (Gv) in the candidate section, a second signal representing a change in the traveling direction magnetic measurement (Gt) in the candidate section, and The above judgment is executed according to the degree of synchronization between the

The operation of the marker detection system 1 configured as described above will be described with reference to the flowchart of marker detection processing in FIG. This marker detection process is a process executed by the marker detection system 1 each time the vehicle 5 advances by 5 cm. The contents of the marker detection process will be described below, mainly focusing on the operation of the detection unit 12 .

The detection unit 12 takes in the magnetic measurement value of each magnetic sensor Cn of the sensor unit 11 every time the vehicle 5 advances 5 cm. The detection unit 12 detects that the vehicle 5 has advanced 5 cm by processing the pulse signal input from the vehicle speed sensor. The detection unit 12 uses, as the magnetic measurement value of each magnetic sensor Cn, a magnetic measurement value representing the magnitude of the magnetic component in the traveling direction (magnetic measurement value in the traveling direction, Gt) and the magnitude of the magnetic component in the vertical direction. A magnetic measurement value (magnetic measurement value in the vertical direction, Gv) is taken in (S101). The detection unit 12 writes the magnetic measurement values (Gt, Gv) of each magnetic sensor Cn fetched from the sensor unit 11 to the work area (RAM storage area) at any time. At this time, the latest magnetic measurement values (Gt, Gv) are newly stored, while the oldest magnetic measurement values (Gt, Gv) are erased. As a result, time-series magnetic measurement values (Gt, Gv) for the past 10 m are stored and held in the work area for each magnetic sensor Cn.

In the traveling direction when the vehicle 5 passes the magnetic marker 10, Gv (magnetic measurement value in the vertical direction) changes as illustrated in FIG. Gv gradually increases as the magnetic marker 10 is approached, and reaches a peak when the magnetic sensor is positioned directly above the magnetic marker 10 . Then, it gradually becomes smaller as the distance from the magnetic marker 10 increases. The change curve of Gv in the traveling direction becomes like a normal distribution curve. In addition, the same drawing is an example in which the N pole of the magnetic marker 10 faces upward. The filled triangles in the figure indicate the position of the magnetic marker 10 in the traveling direction, more strictly the position of the center of the magnetic marker 10 .

In addition, in the traveling direction when the vehicle 5 passes the magnetic marker 10, Gt (magnetism measurement value in the traveling direction) changes as illustrated in FIG. Gt gradually increases as it approaches the magnetic marker 10 and reaches a positive peak at a position before the magnetic marker 10 . As the magnetic marker 10 is further approached, Gt gradually decreases and becomes zero when the magnetic sensor is positioned right above the magnetic marker 10 . This is because the orientation of the magnetic component in the direction of travel is reversed on either side of the magnetic marker 10 . As the distance from the magnetic marker 10 increases, Gt (absolute value) gradually increases on the negative side and reaches a peak. Further, when the distance from the magnetic marker 10 increases, Gt (absolute value) gradually decreases and approaches zero. A change curve in the traveling direction of Gt is a curve in which two positive and negative peaks are adjacent to each other with the magnetic marker 10 interposed therebetween, as shown in FIG. The change curve of Gt produces a zero crossing Zc that crosses zero with a steep slope just above the magnetic marker 10 .

The detection unit 12 first refers to the work area of the RAM and reads the time series data of Gt of each magnetic sensor Cn (Fig. 6). As described with reference to FIG. 6, when the sensor unit 11 reaches right above the magnetic marker 10 while the vehicle 5 is running, the positive and negative of the change curve of Gt by the magnetic sensor positioned above the magnetic marker 10 are A reversing zero cross Zc occurs. The detection unit 12 attempts to detect a zero cross Zc on the change curve of Gt by each magnetic sensor Cn (S102). The filled triangles in the figure indicate the position of the magnetic marker 10 in the traveling direction, more strictly the position of the center of the magnetic marker 10 .

When the detection unit 12 can detect the zero cross Zc (S102: YES), the detection unit 12 sets a predetermined section based on the position in the traveling direction corresponding to the zero cross Zc as a candidate section to which the magnetic marker 10 is highly likely to belong. (S103). In this example, as shown in FIG. 7, a section extending 1 m before and after the position of the zero cross Zc is set as the candidate section.

Subsequently, the detection unit 12 refers to the work area of the RAM and reads out Gv (magnetic measurement value in the vertical direction) in the candidate section. Then, for the time-series data of Gv in the candidate section, the difference between temporally adjacent data is obtained. This time difference corresponds to the time differentiation of Gv in FIG. 5 (an example of differentiation processing). According to this time difference, the change curve of Gv in FIG. 5 is converted into the change curve illustrated in FIG. The filled triangles in the figure indicate the position of the magnetic marker 10 in the traveling direction, more strictly the position of the center of the magnetic marker 10 .

The change curve of the time difference value of Gv in FIG. 8 exhibits the same tendency as the change curve of Gt (the magnetic measurement value in the traveling direction) illustrated in FIG. The time difference value of Gv in FIG. 8 gradually increases as the center position of the magnetic marker 10 is approached, similarly to the change curve in FIG. As the center position of the magnetic marker 10 is further approached, the time difference between the magnetic measurement values in the vertical direction gradually decreases, and becomes zero when the magnetic sensor is positioned right above the magnetic marker 10 . As the distance from the center position of the magnetic marker 10 increases, Gv (absolute value) gradually increases toward the negative side and reaches a peak. Further, the time difference value (absolute value) of Gv gradually decreases and approaches zero as the distance from the magnetic marker 10 increases. The change curve of the time difference value of Gv (FIG. 8) is a curve in which two positive and negative peaks are adjacent to each other with the center of the magnetic marker 10 interposed therebetween, as in FIG. Also, the change curve of the time difference value of Gv has a zero crossing Zc that crosses zero with a steep slope just above the magnetic marker 10 .

The detection unit 12 detects the change curve of Gt (first signal, FIG. 7) in the candidate section set in step S103 above and the change curve of the time difference value of Gv (second signal, FIG. 7) in the same candidate section. 8) A correlation coefficient representing the degree of correlation (an example of the degree of synchronization) between and is calculated (S104). In calculating the correlation coefficient, it is preferable to carry out a normalization process in which the amplitude of the two target change curves is set to 1 in advance. By normalizing the two change curves, it is possible to obtain a normalized correlation coefficient that has a correlation coefficient of 1 when there is a perfect match. A correlation coefficient is an example of a numerical value representing the degree of synchronization between the first signal and the second signal.

The detection unit 12 performs threshold processing on the correlation coefficient (normalized correlation coefficient) obtained in step S104, and determines the degree of synchronization between the change curve of Gt and the change curve of the time difference value of Gv. Specifically, when the normalized correlation coefficient is 0.8 or more (S105: YES), the detection unit 12 determines that the two change curves are highly synchronized. Then, if the degree of synchronization between the two change curves is high, the detection unit 12 determines that the magnetic marker 10 has been detected in the candidate section, and confirms the detection result to that effect (106).

When the detection of the magnetic marker 10 is confirmed, the detection unit 12 measures the amount of lateral displacement of the vehicle 5 with respect to the detected magnetic marker 10 (S107). Then, the detection unit 12 outputs the detection result including the fact that the magnetic marker 10 has been detected and the amount of lateral displacement with respect to the magnetic marker 10 as the result of the marker detection process (S108). The vehicle ECU 50 utilizes the detection result output by the detection unit 12 to implement driving support control such as lane keeping running.

Here, a method for measuring the amount of lateral deviation of the vehicle 5 by the detection unit 12 will be described with reference to FIGS. 9 and 10. FIG. For example, the change curve (distribution curve) of Gv (magnetic measurement value in the vertical direction) of each magnetic sensor Cn of the sensor unit 11 becomes a curve as shown in FIG. 9, for example. The peak of this change curve, that is, the peak in the vehicle width direction, appears corresponding to the center position of the magnetic marker 10. FIG. The filled triangles in FIGS. 9 and 10 indicate the position of the magnetic marker 10 in the vehicle width direction, more strictly the position of the center of the magnetic marker 10 .

In this example, for Gv of each magnetic sensor Cn of the sensor unit 11, the difference between the magnetic measurement values of two adjacent magnetic sensors, that is, the magnetic gradient in the vehicle width direction is obtained. The change curve (distribution curve) of the magnetic gradient in the vehicle width direction is a curve in which positive and negative peaks are adjacent to each other via the zero cross Zc, as illustrated in FIG. In the vehicle width direction, the direction of the magnetism is reversed depending on which side of the magnetic sensor is located with respect to the center position of the magnetic marker 10, and the magnetism is a positive magnetic gradient that increases the magnetism, or a negative magnetic gradient that the magnetism decreases. This is because the Therefore, the zero cross Zc in the figure appears corresponding to the center position of the magnetic marker 10. FIG.

The center position of the magnetic marker 10 in the vehicle width direction can be identified based on FIG. 10 exemplifying the change curve of the magnetic gradient in the vehicle width direction. For example, if the zero cross Zc at which the polarity of the magnetic gradient in the vehicle width direction is reversed is located between any two magnetic sensors Cn, the intermediate position is the center position of the magnetic marker 10 in the vehicle width direction. Become. For example, if the magnetic gradient in the vehicle width direction is zero at the position of a certain magnetic sensor, and the positive and negative of the magnetic gradient in the vehicle width direction are reversed at the positions of the magnetic sensors on both outer sides, the central magnetic sensor is the center position of the magnetic marker 10 in the vehicle width direction.

The detection unit 12 measures the positional deviation of the center position of the sensor unit 11 (for example, the position of the magnetic sensor C8) from the magnetic marker 10 in the vehicle width direction as the amount of lateral deviation of the vehicle 5. For example, in the case of FIG. 10, the position of the zero cross Zc is a position corresponding to C9.5, which is midway between C9 and C10. Since the distance between the magnetic sensors C9 and C10 is 10 cm as described above, the amount of lateral deviation of the vehicle 5 with respect to the magnetic marker 10 is (9.5-8 )×10 cm.

As described above, in the system 1 of the present example, the first processing that focuses on the change in the traveling direction of Gt (the magnetic measurement value in the traveling direction) and the degree of synchronization between Gt and Gv (the magnetic measurement value in the vertical direction) The magnetic marker 10 is detected with high certainty by a combination of the second processing of interest. According to the first process, the candidate section to which the magnetic marker 10 is likely to belong can be set with high certainty with little omission according to the zero crossing Zc at which the positive/negative reversal of Gt occurs.

Furthermore, according to the second process, in the candidate section set by the first process, based on the degree of synchronization between the change in the traveling direction of Gt and the change in the traveling direction of Gv, It can be determined whether or not the magnetic marker 10 has been detected by By determining whether or not the magnetic marker 10 has been detected in the candidate section by the second process, even if there is an erroneous detection by the first process, the erroneous detection can be eliminated with a high degree of certainty.

In the second process of this example, the degree of correlation (normalized correlation number) is obtained as the degree of synchronization between the two change curves. Instead of this, it is also possible to detect the magnetic marker 10 by obtaining the degree of synchronization between the curve of change in the direction of travel of Gt (FIG. 7) and the curve of change in the direction of travel of Gv (FIG. 5). As the degree of synchronization, for example, it is also possible to specify the time lag between the time point of the zero crossing Zc of the change curve in FIG. 7 and the time point of the peak time of the change curve in FIG. As the degree of synchronization, it is also possible to specify the deviation between the frequency or period of the change curve in FIG. 7 and the frequency or period of the change curve in FIG. When obtaining the frequency or period shift of the change curve as the degree of synchronization, the change curve in FIG. 7 and the change curve in FIG. (phase difference), etc. may also be specified. When obtaining the degree of synchronization such as time shift, frequency shift, period difference, period shift (phase difference), etc., for example, the magnetic marker 10 is placed in the candidate section by threshold processing for the amount of shift or the value of the difference. It is possible to determine whether or not the magnetic marker 10 has been finally detected by determining whether or not it belongs to.

This example exemplifies a magnetic sensor capable of measuring a magnetic component in the traveling direction and a magnetic component in the vertical direction. The magnetic sensor may be capable of measuring magnetic components in any two directions out of the magnetic component in the traveling direction, the magnetic component in the vehicle width direction, and the magnetic component in the vertical direction. For example, when a magnetic sensor capable of measuring the magnetic component in the vehicle width direction and the magnetic component in the traveling direction is employed, the magnetic sensor in the vehicle width direction output from the magnetic marker 10 slightly displaced in the vehicle width direction. It is advisable to pay attention to the change curve in the traveling direction of the magnetic measurement value (Gh). As illustrated in FIG. 11, this change curve has a peak when positioned right beside the magnetic marker 10, and becomes a curve that gradually decreases before and after the peak. The change curve illustrated in FIG. 11 has the same tendency as the change curve of the traveling direction of Gv in FIG. Therefore, in the case of the change curve of the traveling direction of Gt and the change curve of the traveling direction of Gh, it is possible to examine the degree of synchronization by a method substantially similar to the method described in this example. The filled triangles in the figure indicate the position of the magnetic marker 10 in the traveling direction, more strictly the position of the center of the magnetic marker 10 .

In addition, it is also possible to measure the magnetic components along the vertical axis, which is the axis perpendicular to the traveling direction, and the vehicle width direction axis. For example, in the case of the change curve of the traveling direction of Gv ( FIG. 5 ) and the change curve of the traveling direction of Gh ( FIG. 11 ), both curves become peaks at the time of passing the magnetic marker 10 . . If it is a combination of these change curves, it is possible to examine the correlation coefficient as it is. In setting the candidate section in the first process, it is also possible to obtain the time difference of Gv (FIG. 8) or the time difference of Gh and detect the zero crossing.

Furthermore, it is also possible to adopt a magnetic sensor that can measure the magnetic component along the traveling direction axis, the magnetic component along the vehicle width direction axis, and the magnetic component along the vertical axis. In this case, by examining the degree of synchronization of the measured values of the magnetic components in the three directions, the accuracy of the second process can be further improved. For example, the correlation coefficient between the change curve of the traveling direction of Gv (FIG. 5, an example of the first signal) and the change curve of the traveling direction of Gh (FIG. 11, an example of the second signal) is the degree of synchronization. In addition to obtaining as It is also possible to obtain the degree of synchronization with at least one of the directional change curves (FIG. 11, an example of the second signal). Then, threshold processing may be performed for each of these two degrees of synchronization, and it may be determined that the magnetic marker 10 has been detected when both threshold processing results in affirmative determination. At this time, the signal obtained by performing differentiation processing on the change curve of the traveling direction of Gv (FIG. 5, an example of the first signal) or the change curve of the traveling direction of Gh (FIG. 11, an example of the second signal) , Gt in the traveling direction (an example of the third signal in FIG. 6) may be obtained as the degree of synchronization.

It should be noted that it is not an essential requirement that the direction of magnetism detected by the magnetic sensor strictly match the traveling direction, vehicle width direction, or vertical direction. Moreover, it is not an essential requirement that the directions of magnetism detected by the magnetic sensors are orthogonal to each other. A plurality of detection directions (detection axes) by the magnetic sensor need only intersect each other.

In addition, in this example, a positional section in the traveling direction is exemplified as a candidate section to which the magnetic marker 10 is likely to belong. Instead of this, it is also possible to set temporal segments as candidate segments. For example, a predetermined period including the point of time of zero crossing Zc in FIG. 6 may be set as the candidate section. The predetermined period may be changed according to, for example, the vehicle speed. For example, it may be a short period on expressways and a long period on general roads where the vehicle speed is low.

Although the specific examples of the present invention have been described in detail above as examples, these specific examples merely disclose an example of the technology included in the scope of claims. Needless to say, the scope of claims should not be construed to be limited by the configurations and numerical values of specific examples. The scope of claims encompasses techniques in which the above specific examples are variously modified, changed, or appropriately combined using known techniques and knowledge of those skilled in the art.

1 Marker detection system (system)
10 magnetic markers 100 lanes (tracks)
100S road surface 11 sensor unit Cn magnetic sensor 110 signal processing circuit 12 detection unit (first circuit, second circuit)
5 vehicle 50 vehicle ECU

Claims

A method for detecting magnetic markers disposed on a road surface forming a surface of a track while a vehicle equipped with a magnetic sensor is traveling on the track, comprising:
The magnetic sensor is capable of measuring magnitudes of magnetic components acting along a plurality of axes including at least two axes for each of the plurality of axes,
A candidate section, which is a temporal or spatial section to which the magnetic marker is likely to belong, based on a change in the traveling direction of the vehicle in the magnitude of the magnetic component along at least one of the plurality of axes. a first process of identifying
A first signal representing a change in the candidate interval of the magnitude of the magnetic component acting along one of the two axes and the candidate interval of the magnitude of the magnetic component acting along the other axis. and a second process of determining whether or not the magnetic marker is detected in the candidate section according to the degree of synchronization.
2. The method according to claim 1, wherein in the second processing, the degree of synchronization is quantified and threshold processing is performed, and when the numerical value representing the degree of synchronization is equal to or greater than a predetermined threshold, the magnetic marker is detected in the candidate section. A magnetic marker detection method for determining that the
The magnetic marker detection method according to claim 1 or 2, wherein the one axis and the other axis are orthogonal to each other.
4. The apparatus according to any one of claims 1 to 3, wherein the one axis is an axis in the direction of travel, and the other axis is an axis perpendicular to the direction of travel,
The second processing obtains a correlation coefficient representing a degree of correlation between the first signal and a signal obtained by performing differentiation processing on the second signal as a numerical value representing the degree of synchronization. A magnetic marker detection method that is processing.
4. The apparatus according to any one of claims 1 to 3, wherein both of the two axes are perpendicular to the traveling direction,
The second processing is a method of detecting a magnetic marker, wherein a correlation coefficient representing the degree of correlation between the first signal and the second signal is obtained as a numerical value representing the degree of synchronization.
4. The apparatus according to any one of claims 1 to 3, wherein both of the two axes are perpendicular to the traveling direction,
The magnetic marker is capable of measuring the magnitude of the magnetic component along the traveling direction axis in addition to the two axes,
In the second processing, a first signal representing a change in the candidate section in magnitude of a magnetic component acting along one of the two axes and a magnetic component acting along the other axis a second signal representing the change in said candidate interval of the magnitude of
a third signal representing a change in the candidate interval in the magnitude of a magnetic component acting along the traveling axis; and at least one of the first signal and the second signal; A magnetic marker detection method that obtains the degree of synchronization of
In claim 6, the second processing obtains a correlation coefficient representing the degree of correlation between the first signal and the second signal as a numerical value representing the degree of synchronization,
a correlation coefficient representing a degree of correlation between a signal obtained by performing differentiation processing on at least one of the first signal and the second signal and the third signal; A magnetic marker detection method, which is a process of obtaining a numerical value representing the degree of
A system for a vehicle equipped with a magnetic sensor to detect a magnetic marker disposed on a road surface forming a road surface,
The magnetic sensor is capable of measuring magnitudes of magnetic components acting along a plurality of axes including at least two axes for each of the plurality of axes,
A candidate section, which is a temporal or spatial section to which the magnetic marker is likely to belong, based on a change in the traveling direction of the vehicle in the magnitude of the magnetic component along at least one of the plurality of axes. a first circuit that identifies
A first signal representing a change in the candidate interval of the magnitude of the magnetic component acting along one of the two axes and the candidate interval of the magnitude of the magnetic component acting along the other axis. and a second circuit for determining whether a magnetic marker has been detected in the candidate section according to the degree of synchronization of the second signal.
8. In claim 8, the second circuit quantifies the degree of synchronization and performs threshold processing, and detects the magnetic marker in the candidate section when the numerical value representing the degree of synchronization is equal to or greater than a predetermined threshold. system that determines that